1. Field of the Invention
This invention relates to methods for recirculating excimer gas in gas lasers. More particularly, this invention relates to improvements in the drive couplers and bearing assemblies used to support rotary fans and axial compressors within the excimer gas environment.
2. Description of the Related Art
Electrically excited gas lasers consist in pertinent part of a pair of electrodes defining a channel, an external power supply connected to the electrodes to create an electric discharge within the channel, and a suitable gas medium which encounters the channel and is excited by the electric field within the channel to effect the lasing operation. After the gas medium within the channel has left an excited state, the gas must be circulated from the channel and through the laser housing to remove excess heat and molecular byproducts which result from the gas excitation. In the past, rotary fans or axial compressors, which required conventional rotary mechanical bearings to support the fans or compressors, have been used to circulate the gas through the housing.
The pumping operation of the gas medium within the laser housing has posed considerable problems in prior gas lasers. The rotary mechanical bearings, required by the conventional rotary fans and axial compressors to support the fan on the laser housing while the fan circulated the gas medium within the laser, required organic lubricants in order to properly operate for the life of the laser. Unfortunately, the organic lubricants necessary for the operation of the bearing assemblies hindered the efficient operation of the laser by depleting the working gas medium within the laser housing, resulting in significant laser power losses.
An additional problem attributable to the presence of organic lubricants in the laser gas environment involves the bake-out process desirable during manufacture of the gas lasers to extend the operating life of the laser. In manufacturing sealed lasers, it is desirable that the laser housing be subjected to a high temperature vacuum bake out to ensure that contaminants which may have been adsorbed by the walls of the laser housing are removed. When bearing lubricants are present in the laser housing during this bake-out procedure, the bearing lubricant vaporizes and contaminates the internal surfaces of the laser, causing a reduction in the operating life of the laser. Moreover, after the bake-out, the bearings are then left without the lubrication they need to operate for the useful life of the laser.
Some methods have been suggested to eliminate the use of lubricants in the fanning apparatus of lasers. Affleck, U.S. Pat. No. 4,751,713, discusses the problems associated with bearing lubricants and discloses the use of a piezo-electric fan to eliminate the need for bearing lubricants. In Affleck, a piezo-electric fan, comprising two counter-oscillating flexible blades, is driven at resonance by a bimorph comprising two piezoceramic bending elements. The bimorph elements alternatively expand and contract when they are electrically energized, which oscillates the flexible blades to blow the gas medium within the laser housing by fanning action, rather than by rotary action. Using the piezoelectric fan, no wearing elements are present within the laser housing and no lubricants are necessary. Thus, the contamination problems associated with the bearing lubricants are eliminated.
An additional method of avoiding the use of bearing lubricants is by supporting the bearings with high pressure laser gas medium as disclosed in application Ser. No. 07/301,870 to Murray et al, filed May 26, 1988 and commonly owned herewith. By injecting the gas medium into channels within the bearing, the gas medium, itself, substantially frictionlessly supports the bearing, eliminating the need for a contaminating external lubricant.